Currently, there are two principal areas of focus in our laboratory. One involves structure determination of membrane proteins at atomic resolution by electron crystallography. Projects underway include crystallization and structure determination of the oxalate carrier OxlT (in collaboration with Prof. Peter Maloney at Johns Hopkins University School of Medicine, and Dr. Jacqueline Milne, NCI), and electron crystallographic analysis of light-induced conformational changes in the proton pump bacteriorhodopsin (in collaboration with Dr. Richard Henderson, MRC Cambridge, England). Over the course of the last year we have initiated systematic efforts to obtain crystals of OxlT suitable for high resolution analysis. We have also made substantial progress towards structure determination of the cytoplasmically open conformation of bacteriorhodopsin. Over the next year, we expect to refine this structure to a resolution of ~ 3.0 Angstroms, and to present a complete stereochemical mechanism which explains the structural basis of proton pumping by bacteriorhodopsin. A second area of research involves structure determination of large protein complexes by analysis of images of single particles obtained by high resolution electron microscopy. Using the 1,800 kD complex of the core domain of pyruvate dehydrogenase as a model molecule, we are establishing methods to carry out such an analysis at high resolution (in collaboration with Dr. Jacqueline Milne, NCI). We have already obtained a three-dimensional reconstruction of the core domain complex at a resolution of about 15 Angstroms, and expect to improve it further over the course of the next year.